There is a growing public awareness of, and concern for, the health effects attendant contact with air-borne microorganisms. The concern is particularly acute as regards the air quality in enclosed spaces, such as home and workplace. Workplaces including breweries; pharmaceutical manufacturing, formulation and encapsulation sites; hospital critical areas such as surgery and intensive care units; and semiconductor manufacturing sites are all very susceptible to disruption by the presence of various airborne microorganisms.
As many homes and workplaces are already equipped with air conditioning systems, it would be convenient if means were available for operating an air-conditioner in a manner lethal to airborne microorganisms.
Open-cycle air-conditioners are known in the art and are based primarily on the Munters Environmental Control system (MEC) unit as described in U.S. Pat. No. 2,926,502. As set forth in this patent, the basic open-cycle air-conditioner operates by dehumidification and subsequent cooling of air wherein moist hot air is conditioned by basically a multistage process to produce cool air.
In open-cycle air-conditioning systems, a basic multistep approach is used. In the inlet path, outside air is subjected to removal of moisture through a moisture transfer wheel, with the dried air being cooled by means of a heat exchanger wheel with the subsequent addition of moisture by an evaporative element so as to further cool the air before it enters the area to be conditioned. In the return cycle, the air passes through an exhaust path which includes a further evaporative element, the heat exchanger wheel, a heating element, and the moisture transfer wheel, after which the air is exhausted to the atmosphere. In the return cycle, also called the outlet path, air passing through the moisture transfer wheel accomplishes the regeneration of the wheel by driving moisture therefrom.
One of the major advantages of this type of system is that a constant supply of fresh, filtered air is delivered to the space to be conditioned as opposed to the recirculation of air as is found in standard heating and cooling systems.
The basic principle of the MEC system is that dry warm air can be simultaneously cooled and humidified by contacting it with water vapor. However, in geographic areas where the air is both warm and humid, it must be dried before it can be cooled by evaporation. The efficiency and the effectiveness of an open-cycle air-conditioning system depends upon the ability of the unit to dehumidify the warm moist air input, and upon the effectiveness of the heat exchanger wheel or unit.
As to the heat exchanger wheel, operation depends upon the opposite faces remaining at different temperatures. This means that there must be a significant temperature gradient across the wheel in the axial direction. Proposed use of highly thermally conductive material such as metal results in the temperature gradient through the wheel being substantially less, with poor heat exchange and low effectiveness. In the open-cycle air-conditioner system, the heat created by the drying of the air by the moisture transfer wheel must be removed by the heat exchanger wheel. However, migration of the heat axially in the direction of flow of the air through the wheel must be kept to a minimum. If the heat does not migrate, the air stream to be treated exiting from the heat exchanger wheel will not be sufficiently cooled to render the system practical for air-conditioning reasons because the evaporator would not be capable of reducing the higher temperature to an acceptable level of temperature and humidity.
There is a need in the art for an effective air conditioning system that treats air so as to accomplish a substantial reduction in the concentration of air-borne microorganisms, where the treatment is accomplished without exposing the air to toxic chemicals. The present invention solves this need by providing a desiccant air conditioning system which employs a zeotite desiccant. Use of the present invention results in a safe and highly effective method for substantially reducing air-borne microorganisms, while at the same time providing temperature control and dehumidification of air.